Color blindness chart for detecting anomalous vision, deuteranopes, protanopes, tritanopes, and monochromats



NOV. 9, 1948. R, B, MORR|S 2,453,335

COLOR BLINDNESS CHART FOR DETECTING ANOMALOUS VISION, DEUTERANOPES, FROTANOPES,

TRITANOPES AND MONOGHROMATS- Filed oct. 27, 1.944 2 vsheetsrshee' 1 mi BZ L-rb,

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TRITANOPES, AND MONOGHROMATS Filed 061.27, 1944 2 sheets-'sheet 2 Reginald lbrd Morris nventor A l tome y Patented Nov. 9, 1948 COLOR BLINDNESS CHART FOR DETECTING ANOMALOUS VISION, DEUTERANOPES, PROTANOPES, TRITANOPES, AND MONO- CHROMATS Reginald Burford Morris, Wealdstone, England,

assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application October 27, 1944, Serial No. 560,628 In Great Britain November 9, 1943 This invention relates to apparatus for use in testing colour blindness.

On examining a spectrum the majority of people can recognise easily the differences in colour between green, yellow, and red. minority of people, however, there is some inability to distinguish between these colours, and such people are referred to as "colour blind. One of the tests capable of giving an accurate quantitative description of the type of colour blindness is provided by the Nagel "Anomaloscope. This is an optical instrument in which the observer is confronted with two adjacent bright coloured patches, one of which is illuminated with spectral yellow light, and the other is illuminated with a mixture of spectral green and spectral red. The patch illuminated by the mixture of the green and red can be made to appear the same colour as the yellow patch by suitable adjustment (means for which is provided onthe instrument) of the ratio of intensity of the red to intensity of the green; and in use the observer has to so adjust the ratio as to effect, what seems to him, a match in colour betweenthat mixture and the spectral yellow patch. Most people Vdol require both red and green in order to effect a match between the mixture and the spectral yellow and may be called trichromats. It happens that a majority of these trichromats require a ratio between the red and the green which is not markedly different among the people in this majority; the people of this majority are classifled as norma-l. Of the broad class of people who require both the red and the green to match the yellow (i. e, the trichomats) some require a.

markedly different ratio of the red to the green than those people who are classified as normal These people are called anomalous Besides these normal and anomalous people there is a small proportion of people falling in the class known as dichromates who can use either the red or the green to eiiect a match with the yellow. These latter people are colour blind and there are two classes of them; a characteristic of the people of the one class is that they require the red to be of moderate intensity compared with the intensity of the yellow, and are termed deuteranopes, while the other class requires the red to be of considerably higher intensity compared with the intensity of the yellow, andk are 4 Claims. (Cl. 88-20) called protanopes There is also a third class of dichromats termed tritanopes who have a characteristic not shared by the protanopes and deuteranopes, in that a blue appears to them to match with a blue-green providing theapparent brightnesses are equal. Then there are people who are classied as monochromats about whom little knowledge is available, but it seemsr that their luminosity curves are similar to the luminosity curves of deuteranopes or protanopes or they may be cone-blind, wearing dark glasses, and using only scotopic vision. An article on Monochromatism by F. H. G. Pitt appears in Naturef volume 154, pages 466 to 468, 1944, in

which the probability of incidence of these monochromatic types is calculated.

People who are either deuteranopes or protanopes can be distinguished by many wellknown tests, but the distinguishing of people who are anomalous to' an important degree is not' easy, although a test for them is provided :by the Nagel anomaloscope. It is important that such people should be distinguishable, since they have,v for instance, some disability in recognising red and green signal lights, and are under a disadvantage in any Work which requires accurate colour matching. Many people who have little familiarity with the use of optical instruments nd difficulty in operating it to secure a colour match, and despite its merits in other respects, has not, for this reason come into general use.

The object of the present invention is to provide an apparatus which can be used in tests for anomalous people, as well as the truly colour blind, but'with the advantage that it can be used satisfactorily by people under test for colour blindness who are not necessarily skilful in colour matching with optical instruments. Inthe preferred form of the present'invention the apparatus is one which can be used for the purpose of distinguishing people who are normal,f'and all the above types of colour blindness.

According to the present invention there is" provided an apparatus for testing colour discrimina- Vtion of a human eye which' comprises at vleast three pairs of coloured patches each patch-of which emits light only from one or two of three bands in the visible spectrum chosen such that to normal people the two outer bands can be mixed to match the middle band, and each pair green.

' of people.

of patches being such that one patch of the pair emits only the middle waveband and the other patch of that pair emits at least one of the outer two wavebands but not the middle band, the proportions ef light in such outer two wavebands being different for the different patches emitting them, there being at least one pair of which one patch emits both said outer two wavebands.

The said three bands can consist of three different very narrow Wavebands. It is desirable to employ more than one pair which has a patch which emits both said other two wavebands and: then to make the ratio of the emissions of said other two bands different forlthe different pairs. If there is more than one pair of patchesin which.

should differ in the ratio of the intensity of the red, compared with the yellow.

The three substantially monochromatic wave' bands which we prefer to employ-are as followst( (1) A waveband having its maximum emission within the range 520 to 550ml/1 and such that atp-VV 'f' those two wavelengths the emission Ais not more than one-tenth of that at the maximum. This;I

we term herein substantially monochromatic Preferably the maximum should be within 525 to 540 ,ma for instance at 530 mn. v

(2) A waveband having its maximum emission within the range 570 to 600 ma and such that at those two wavelengths the emission is not more .than one-tenth of that at the maximum. This we term herein substantially monochromatic yellow. Preferably the maximum should be within 580 to 590, for instance at 585 mfr.

,(3) Avwaveband having its maximum emissionwithin the visible range` above 600 maand such vthat atv 60G my. the visual brightness is not more thanone-tenth that at the maximum. This we Yterm herein substantially monochromatic red.

Preferably the maximum should be within 6x50 tok 700, for instance at 680 mp..

In a preferredl form of the invention, a series of at least five pairs are employed having the vfollowing natures.

(1) Patch of substantially monochromatic yellow. Patch of substantially monochromatic red of. about the same brightness as the yellow, to

themajority of people.

(2) Patch of substantially monochromatic yellow. Patch of mainly substantially monochro-vv matic red plus a small proportion of substantially vmonochromatic green,ri. e. a smaller proportion than in the third pair, so that the patch appears more red than the yellow patch to the majority of people.

(3) Patch of substantially monochromatic yellow. Patch of substantially monochromatic red plus substantially monochromatic green in a proportion such that the patch appears of about the same colour as the patch of yellow to the majority,

. (4) Patch of substantially monochromaticv yelylow.- Patch of mainly substantially monochromatic green plus a small proportion of substantiallymonochromatic red, i. e. a smaller propor-,f 4v

tion than in the third pair, so that the patch appears more green than the yellow patch to the majority of people.

A(5) Patch of substantially monochromaticyellow. Patch of substantially monochromatic red.

of vhigher intensity than first pair.

People who consider pair 3 to'match in colour the patch of red inf the `better than'any others are normal People who consider pair 2 or paire to matchin colour-better.;

. one of each pair contains the-red only, then'vthese f 'detect the tritanopes or by matching a blue with a yellow, for brightness to identify the three monochromaticitypes.

Fig.`.1 is a perspective sketch of an yapparatus incorporating vlthe invention.

Figs. 2, 3, and 4 are spectrophotometric curves l ofthe light transmitted by the filters used in the windows or patches are arranged 1n series. Some apparatus shown in Fig. 1.

Fig. 5 is the cross section of a color filter. l Y Fig- `6 is thecross section of two superimposed color filters.

Avery useful apparatus consists of that shown in vFigure 1 of the drawings attached hereto which employsiifteen pairswhich, by wayr of example, can'be made with transparent lters as follows. A housing I about 12" x l0 on its face and lhaving a Watt gas-filled pearled tungsten electric lamp situated as shown at 2 is provided with an opal glass on which is superimposed an opaque plate 3 having fifteen pairs of rectangular openings as shown, and in each opening fastened one of the pairs of patches in order shown by the numbers 1 ton9 and letters A, BC D, E, F, ,on the drawing. Essentially the embodiment of the invention shown in Fig. l is thus aboxwith a light inside it which more or less uniformly illuminates 30 color filters arranged aswindows on one side, namely, the front side thereof. The

observersl see the patches matching each other in one pair, whereas other observers see the patches vas different colors in that particular pair but Y matching in another pair.

yPatches la, 2a, etc. to 9a are all spectral yellow and actually appear to the normal eye as very dark yellowish. The apparentV color of the forthfin the following table:

patches, to. the so-called normal. personk is set Patcha Patch b very dork yellowish very dark brownish maroon. do very dark brownish orange. .do very dark brownish yellow orange.

very dark brownish yellow. very dark yellowish. very dark yellowish green. verylark green.

Do. Y bright red. dark yellowish (slightly bright red (darker).

lighter). bright (cyan) blue dark yellow1sh (lo bright green.

bright blue.A bright blue (darker).

,bright blue (still darker).

In eachpair, except pair C, the spectral yellow patch. consists of a filter such as shown in Fig. 5

' madeof a mixture of Eosin 2524 and Naphthol GreenI BNS while the other patch of the rst nine pairs is dichroi'c and is made of a lter transmitting only.v the red and the green and consisting of' V014-54 mgm. per sq. cm. of Soluble BluelAS, and either 1.2 mgms. per square cm. of Tar-trazine N250;and;0.004'5-mgm. Vper-sq. cm. ofFl'uorescein kl0092,or a WrattenV No. 16 ltergover which is superimposed either a copper chloracetate or a Naphthalene Bordeaux B110 filter (to suppress, more or less, either spectral red or spectral green as the case may be) as given inthe following table, wherethe iigures refer to quantities as mgms. per sq. om.

or Col. II may be as follows.

Use standard filters of Eosin 0.73 and Naphthol Green 0.78 with the following neutral grey lters of the following density values.

Optical Pair No. Density Pair A shown as Aa ami All- This pair consists of one patch Aa made of a spectral yellow filter made with Eosin 2524 and Naphthol Green BNS both at 0.66 mgm. per sq. cm., and another patch Ab made of a red filter made with Methyl Violet 28925 at 9.11 mgm. per sq. cm. superimposed such as in Fig. 6, on a yellow lter made with Tartrazine N250 at 1.2 mgrns. per sq. cm.

Pair B shown as Ba and Bb.-This is the same as pair A, except that a neutral grey filter of density 0.53 is superimposed on the red patch to make up Bb.

Pair C shown as Ca and Cb.-This pair consists of one patch Co made of a Wratten No. 75 filter and the other patch Cb of a Wratten No. 75 filter superimposed on a Wratten No. 12 filter. As this pair is for ascertaining tritanopes, the brightness is matched for such a person by the superimposition of a neutral grey of density 1.02 on the first mentioned patch.

Pair D shown as Da and Db.-This pair consists of one patch Db made of a Wratten No. 75 iilter and the other patch Da of a spectral yellow filter as in pair No. of the table. The brightnesses of the two patches have been adjusted to be equal for a person having monochromatic colour vision and a protanopic luminosity curve by the superimposition of a neutral grey lter of density 1.06 to the rst patch.

Pair E shown as Ea and Eb.-This pair consists of one patch Eb made of a Wratten No. '75 filter and the other patch Ea of a spectral yellow filter as in pair No. 5 of the table. The brightnesses of the tWo patches have been adjusted to be equal to a person having monochromatic colour vision and a deuteranopic luminosity aglio 3;;335

curvefbywthe 'superimposition of a neutral grey filter of Vdensity 1.62 to the rst patch.

Pair Fshown as Fa and F11-This pair consists of one patch Fb made of a Wratten No. '75 filter andthe `other` patch Fa of a spectral yellow lter as in pair No. 5 in the table. The brightnesses of the two `patches have been advjusted to be equal to a person having monochromatic colour vision and a scotopic luminosity curve by the 'superimposition of a neutral grey filter of density-2.62 to the first patch.

The reason that the quantities of dyes used for the various spectral yellow patches la, 2a, 3a, 7a, 8a and .9a-are greater at the beginning and end of the series in this table is as follows. The amount of copper Chlor-acetate used for the dichroic filter 5b in pair 5 and also the dyes used for the spectral yellow lter 5a are first chosen so as to give a convenient yellow colour in both of the pairs and also that the colour and brightness should be the same. The particular amounts used here for a normal person results in a chart giving -a high degree of discrimination when testing for colour blindness. Then for a person who is deuteranomalous the amount of copper Chlor-acetate required in patches 6b to 9b to give the ratio of red to green which is necessary in a mixture of these two colours in order to synthesise a yellow similar to the spectral yellow colour 5a to 9a is found to be that given in the table. It will be observed that the colour of all the spectral yellow patches are the same. With this amount of acetate, although the colour matches, the brightness does rnot match and since it is very confusing to try to match colour when vbrightness appears to be different, the brightness of the yellow patch 7a, 8a or 9a is made to give a brightness match; this is done in the above chart by `,using more eosin and naphthol green in 7a, 8a or 9a but it can be done equally well by adding a neutral grey over a patch of the same constitution as the yellow patch in No. 5, as shown in the second table. Similarly the density may be matched for any of the other pairs of pat-ches.

By way of illustration the absorption curves of the patches of Nos. 1, 5 and 9 are given in Figure 2; for instance the portion of the curve of No. 1 which represents the spectral yellow patch is marked la, and the portions representing the other patch are marked 1b which also appears yellow to some observers. The absorption curves of pairs A, B and C are given in Figure 3 and for pairs D, E and Fin Figure 4.

Between the patches in each pair is an opaque strip the purpose of which is to reduce the observersV discrimination to brightness and colour just fors-the pair which should appear to him to be the best match. Itis desirable because untrained observers often show a disinclination to decide on a best match.

In the operation of the above apparatus the lamp is energised in the usual way and the chart is viewed bythe person` to be tested in a darkened or semi-darkened room. The operator rst asks the observer which of the pairs Nos. 1 to v 9 appearto him to be the best match for colour ,and-brightness.

Then he is asked to View the patches A, B and C, and whether any of these appear to him to match for colour and brightness.

Lastly he is asked to view the patches D, E and F, and again is asked Whether any pairs are matched. If he rejects A, B, C, D, E and F then the pair 1 to 9 acceptable defines his colour Acceptance of either D, E or F show monochromatism, D defines a monochromat withv a luminosity curve similar to the protanope, E for a deuteranopic luminosity curve and. F fory a scotopic luminosity curve i. e. showing cone blindness.

Although the various pairs of colour patches can according to the invention be arranged to form al tablet in which al1-the patchesare irremovable from the tablet, it may often be desirable, for any selected pair or pairs of patches,4 Y

to be capable of being removed or masked or for some or all of the pairs to be interchangeable as regards their position in the tablet. The object of this is to prevent one observerv under test from telling another observer known to have abnormal eyesight which pairs he shouldy say are colour matches if he desires to mislead an examiner to the effect that his eyesight is normal.

For instance, the pairs can be arranged in groups of several pairs in a group and several; V

groups being interchangeable, for example if nine pairs are used, these can be made in three groups of three pairs in each group andv such groups can be interchangeable.

All the dyes mentioned herein are sold by.`

Messrs. Imperial Chemical Industries, Limited, and have the following compositions 'with reference to Rowes Colour Index.

Tartrazine N250 Colour Index No. 640 Napthalene Bordeaux B410 Colour Index No. 88

Soluble Blue AS Colour Index No. 707

Napthol Green BNS Colour Index No. 5

Flourescein 10092 This is. composed of Dyestuffs Colour Index Nos. 786 and 768 Eosin 2524 This is composed of Dyestuffs Colour Index Nos. 768 and 774 Methyl Violet 28925 This is composed of'DyestuiTs Colour Index Nos. 680 and 681 What I claim is:

1. A device for testing color discrimination of the human eye, said device having a plurality of pairs of closely adjacent patches ofl color ter materials and including at least three such pairs capable of being transilluminated by white light, one patch of each pair when so illuminated transmitting substantially only a yellow wavelength band of light of wavelength between 570 and 600 my. and appearing yellow to the normal human eye, and the other three patches of said three pairs transmitting both a red wavelength band of light of wavelength about 600 mp and a green wavelength band of light of wavelength between 520 and 550 mu, but not appreciably transmitting said yellow light, or any other VisibleI wavelength bandy exceptthe said'` redy and green wavelengthbands, one of said threev other patches, namely the other patch inv one ofthe three pairs, transmitting `said red and green bands in av proportion such that it4 appearsA to the majority of people as about the same color as the adjacent yellow patch of that pair, another of said three other patches, namely, the other patch in a second one of the threepairs, transmitting a higher proportion ofA red than.in said onebf the three pairs so that it matches its 'yellow patch only for people with anomalous visionv with a degree of red deciency and the third one of said three other patches, namely, the other patch in the third one of the three pairs, transmitting a higher proportion of green than in said one of the three pairs so that it matchesits yellow patch only for people with anomalous vision with a degree of green deciency.

2. Apparatus, according to claim 1 including at least one pair of patches, in addition to the said three pairs of patches in which one patch emits only said yellow band and the other patch emits only said red band.

3. Apparatus according yto claim 1 including an additional pair of patches for detecting'tritanopes consisting of a patch emitting onlysubstantially spectral green and a patch emitting blue green.

4. Apparatus according to claim 1 including an additional pair of patches for detecting monochromats consisting of a patch emitting onlysaid yellow band and a patch emitting substantially spectral blue.

REGINALD BURFORD MORRIS;

REFERENCES CITED rThe following references are, of recordin the le of this patent:

UNITED STATES PATENTS OTHER REFERENCES Rabkin Polychromatic Plates for C0101` Sense Examination, Kiev, State Medical Publ. Board, 1936 (1st ed.) pp. 34, 35', 36 and PlateXVIII.

American Optical Co. Pseudo-Isochromatic Plates :for Testing Color Perception by Beck Engraving Co. 1940 New` York.

The American Weekly Magazine, May 19, 1935,`

page l (shows the conventional Ishihara colorblind test chart).

Helmholtz PhysiologicalrOptics, vol. II, pages 397 to 402, 406 to 409 as translated by Southall` Published, by Optical Soc. of America, 1924.

Zoethout Physiological Optics, 1927, Published, Professional Press Chicago, pages 223 to 226,

ACersrtificate of Correction Patent No. 2,453,335. November 9, 1948.

REGINALD BURFORD MORRIS It is hereby certified that errors appear in the above numbered patent requiring correction as follows:

Column 5, line 53, for Co read Ca; column 7, line 65, claim 1, for the word about read above;

and that the said Letters Patent should be read with these corrections therein thxtt the same may conform to the record of the case in the Patent Ofce.

Signed and sealed this 8th day of March, A. D. 1949.

THOMAS F. MURnHY,

Assistant of'Potene, 

